What kind of bacteria is Legionella?

Legionella pneumophila was first discovered in Philadelphis in 1976.

Legionella’s are Gram –negative bacteria. Most species have the ability to move due to lateral or polar flagella. Each Legionella usually has one to three flagella. Legionella pneumophilia has only one flagell. The flagella, is located in the pole. They do not form spores and they are aerobic bacteria. Legionella’s, usually have a rod – shaped or a coccoid – shaped form. Legionella’s do not form capsule and they are facultative intracellular parasite. Today, there are at least 50 different species of Legionella’s, divided into 70 serological groups. They are always present in the surface of rivers, lakes, pools, tubs, etc.

The genus Legionella, includes species like Legionella pneumophilia which causes the Legionnaire’s disease. Legionella’s have two major life cycles. The first life cycle is called the replicative phase, during which they are non-motile and have a low toxicity. The second life cycle is called the infectious phase, during which the bacteria gets shorter, thicker and with high toxicity. During the second phase flagella’s are formed.

Legionella’s require L-cysteine or iron salts for cultivation. They use amino acids for energy, and are not able to ferment carbohydrates. They are parasitic microorganisms, which are able to grow in the monocytes and alveolar macrophages. The macrophage infectivity protein is the most important virulence factor of Legionella’s, which makes it able for the bacteria to enter, grow and multiply inside the macrophages.  Legionella’s are able to produce different kind of enzymes like metaloprotease, fosfolypase C, etc. Legionella pneumophila feature unique lipopolysaccharide structures on their outer cellular membranes.  These unique chains make the staining of Legionella’s, very difficult.

Sera have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and micro agglutination tests have also been successfully applied. Legionella stains poorly with gram stain, stains positive with silver, and is cultured on charcoal yeast extract with iron and cysteine.

In order for Legionella to survive within macrophages and protozoa it must create a specialized compartment known as the Legionella containing vacuole. Formation and maintenance of the vacuole are crucial for pathogenesis. Once, the bacterium gets inside the host cell it will start to grow and reproduce. It has been discovered that Legionella is a genetically diverse species with 7-11% of genes strain specific.

They can grow at a range of temperatures, anywhere from 5 to 63 degrees Celsius. However, optimal growth occurs between 25 and 40 degrees Celsius.

Humans get infected by inhaling the air which is polluted with Legionella. Until now, no cases have been reported that the disease was spread from human to human.

What is the Legionnaire’s disease?

Legionnaires’ disease is a severe form of pneumonia, caused by Legionella pneumophylia.  It is an serious bacterial infection of the pulmonary tract in humans. Other Legionella species are associated with a disease called Pontiac fever, a systemic illness.

People who are at a greater risk to get infected incudes: tabaco smokers, people with a compromised immune system like HIV/AIDS, organ transplants, etc., people who have a chronic lung disease or any other chronic disease like diabetes, people who are over the age of 50.

The infection occurs from inhalation of the mist from the water, which contains Legionella pneumophilia. The mist usually comes from hot tubes, showers, air conditioning, etc.

It is very difficult to distinguish this disease from any other type of pneumonia.

This can be a very serious and even life threatening disease, but usually most of the people recover with antibiotic treatment.

Legionellosis is used for any disease caused by the Legionella bacteria.


Signs and symptoms of Legionnaire’s disease

The incubation period of Legionnaire’s disease is usually two to ten days. It usually begins with headache, mild to high fever, chills and muscular pain. After a day or two, other signs and symptoms develop like: chest pain, difficulties breathing, shortness of breath, cough, nausea, vomiting, abdominal cramps and abdominal pain, diarrhea, confusion, etc. Other metal changes are possible.

Even though the disease primarily affects the lungs, as the organ where this microorganism first enters, the disease can spread to other parts of the body, including heart, brain, kidneys, liver, etc.

Legionnaire’s disease can lead to some life threatening complications like:

  • Respiratory failure – when the lungs can’t provide the body with enough oxygen.
  • Septic shock – blood pressure suddenly drops and the vital organs like, heart, lungs or brain, are not supplied with enough blood. The heart tries to compensate by increasing the volume of blood pumped, but the extra workload eventually weakens the heart and reduces blood flow even further.
  • Acute kidney failure – which leads to accumulation of waste products in the body.

How is Legionnaire’s disease diagnosed?

Blood tests, Chest X-ray, CT – scans, tests of an sputum or lung tissue samples, and tests that confirm the presence of Legionella antigens help diagnose this disease. The four major methods for diagnosis are:

  • determination of antibody level,
  • demonstration of the bacterium in tissues or body fluids by using immune fluorescent microscopy,
  • isolation of the organism on culture media,
  • detection of antigenuria.

How is Legionnaire’s disease treated?

Treatment of this disease is with antibiotics, like Clarithromycin, Azithromycin, Levofloxacin, etc. They should be started as soon as the disease is suspected or confirmed. This helps prevent serious complications that might occur, if the disease is not treated on time.

Pontiac fever doesn’t require treatment and it resolves on its own without causing any further problems and complications.

There is no vaccine for Legionella.

The best way to prevent an outbreak of Legionnaires’ disease is to ensure any water system is properly maintained. This mainly involves keeping water either cooled below 20ºC or heated above 60ºC. The water supply should also be kept free of any impurities and kept moving so it doesn’t stagnate.